fix(plugin-org): implement batching in useGetEntities to handle large headers

The useGetEntities hook can result in requests to /api/catalog/entities
where the headers exceed the default maximum Node.js header size of 16KB.

This commit implements batching in the useGetEntities hook to handle
cases where this is likely to occur.

Refs: https://github.com/backstage/backstage/issues/22139
Signed-off-by: Beth Griggs <bethanyngriggs@gmail.com>

.changeset/fast-pens-smell.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-org': patch
+---
+
+The `useGetEntities` hook could result in requests to `/api/catalog/entities` where the headers exceed the default maximum Node.js header size of 16KB. The hook logic has been adjusted to batch the requests.

plugins/org/src/components/Cards/OwnershipCard/useGetEntities.test.ts

@@ -231,6 +231,110 @@ describe('useGetEntities', () => {
       );
     });
   });
+
+  describe('useGetEntities with 500+ relations', () => {
+    const manyGroups = Array.from({ length: 555 }, (_, i) =>
+      createGroupEntityFromName(`group${i + 1}`),
+    );
+
+    const givenUserWithManyGroups = {
+      kind: 'User',
+      metadata: {
+        name: givenUser,
+      },
+      spec: {
+        memberOf: manyGroups.map(
+          group => `group:default/${group.metadata.name}`,
+        ),
+      },
+    } as Partial<Entity> as Entity;
+
+    beforeEach(() => {
+      getEntityRelationsMock.mockImplementation(entity =>
+        entity?.kind === 'User'
+          ? manyGroups.map(group => createGroupRefFromName(group.metadata.name))
+          : [],
+      );
+      (catalogApiMock.getEntities as jest.Mock).mockClear();
+    });
+
+    it('should handle 500+ relations without exceeding URL length limits', async () => {
+      const { result } = renderHook(
+        ({ entity }) => useGetEntities(entity, 'aggregated'),
+        {
+          initialProps: { entity: givenUserWithManyGroups },
+        },
+      );
+
+      await waitFor(() => expect(result.current.loading).toBe(false));
+
+      const callArgs = (catalogApiMock.getEntities as jest.Mock).mock
+        .calls[0][0];
+
+      expect(
+        callArgs.filter[0]['relations.ownedBy'].length,
+      ).toBeLessThanOrEqual(100);
+
+      const owners = callArgs.filter[0]['relations.ownedBy'];
+
+      expect(Array.isArray(owners)).toBeTruthy();
+      expect(owners.length).toBeLessThanOrEqual(100);
+    });
+  });
+
+  describe('useGetEntities exceeding default 16384 bytes header size', () => {
+    const largeNumberOfGroups = Array.from({ length: 600 }, (_, i) =>
+      createGroupEntityFromName(`very-long-group-name-${i + 1}`),
+    );
+
+    const givenUserWithLargeNumberOfGroups = {
+      kind: 'User',
+      metadata: {
+        name: givenUser,
+      },
+      spec: {
+        memberOf: largeNumberOfGroups.map(
+          group => `group:default/${group.metadata.name}`,
+        ),
+      },
+    } as Partial<Entity> as Entity;
+
+    beforeEach(() => {
+      getEntityRelationsMock.mockImplementation(entity =>
+        entity?.kind === 'User'
+          ? largeNumberOfGroups.map(group =>
+              createGroupRefFromName(group.metadata.name),
+            )
+          : [],
+      );
+      (catalogApiMock.getEntities as jest.Mock).mockClear();
+    });
+
+    it('should batch the request to avoid exceeding header size limits', async () => {
+      const { result } = renderHook(
+        ({ entity }) => useGetEntities(entity, 'aggregated'),
+        {
+          initialProps: { entity: givenUserWithLargeNumberOfGroups },
+        },
+      );
+
+      await waitFor(() => expect(result.current.loading).toBe(false));
+      const callArgs = (catalogApiMock.getEntities as jest.Mock).mock
+        .calls[0][0];
+
+      const url = new URL(
+        `http://localhost/api/catalog/entities?${new URLSearchParams(
+          callArgs as any,
+        )}`,
+      );
+      const headerSize = url.href.length;
+      expect(headerSize).toBeLessThanOrEqual(16384);
+
+      const owners = callArgs.filter[0]['relations.ownedBy'];
+      expect(Array.isArray(owners)).toBeTruthy();
+      expect(owners.length).toBeLessThanOrEqual(100);
+    });
+  });
 });
 
 function createGroupEntityFromName(name: string): Entity {

plugins/org/src/components/Cards/OwnershipCard/useGetEntities.ts

@@ -143,26 +143,38 @@ const getOwners = async (
   return [stringifyEntityRef(entity)];
 };
 
-const getOwnedEntitiesByOwners = (
+const batchGetOwnedEntitiesByOwners = async (
   owners: string[],
   kinds: string[],
   catalogApi: CatalogApi,
-) =>
-  catalogApi.getEntities({
-    filter: [
-      {
-        kind: kinds,
-        'relations.ownedBy': owners,
-      },
-    ],
-    fields: [
-      'kind',
-      'metadata.name',
-      'metadata.namespace',
-      'spec.type',
-      'relations',
-    ],
-  });
+  batchSize: number = 100,
+) => {
+  const batches = [];
+
+  for (let i = 0; i < owners.length; i += batchSize) {
+    const batch = owners.slice(i, i + batchSize);
+    batches.push(
+      catalogApi.getEntities({
+        filter: [
+          {
+            kind: kinds,
+            'relations.ownedBy': batch,
+          },
+        ],
+        fields: [
+          'kind',
+          'metadata.name',
+          'metadata.namespace',
+          'spec.type',
+          'relations',
+        ],
+      }),
+    );
+  }
+
+  const results = await Promise.all(batches);
+  return results.flatMap(result => result.items);
+};
 
 export function useGetEntities(
   entity: Entity,
@@ -191,13 +203,13 @@ export function useGetEntities(
   } = useAsync(async () => {
     const owners = await getOwners(entity, relations, catalogApi);
 
-    const ownedEntitiesList = await getOwnedEntitiesByOwners(
+    const ownedEntitiesList = await batchGetOwnedEntitiesByOwners(
       owners,
       kinds,
       catalogApi,
     );
 
-    const counts = ownedEntitiesList.items.reduce(
+    const counts = ownedEntitiesList.reduce(
       (acc: EntityTypeProps[], ownedEntity) => {
         const match = acc.find(
           x => x.kind === ownedEntity.kind && x.type === ownedEntity.spec?.type,